----- Original Message ----- > On Mon, Jun 25, 2012 at 03:16:35PM -0700, Jose Fonseca wrote: > > Indeed lp_build_brilinear_lod is not faster than > > lp_build_ifloor_fract, but brilinear is faster, not because log is > > a > > faster approximation, but because it increases the odds that fract > > part is zero, which means that we can sample from a single mip > > level, instead of lerping between two mip levels. > > > > I think you have a good point here -- lp_build_brilinear_lod is a > > log2 approximation which is wrong here and that's a great catch, -- > > but I have a point too: lp_build_ifloor_fract will slow down > > texture > > sampling. > > > > Just like log2 and brilinear log2, we need a variant of > > ifloor_fract, that increases the probability of fract part being > > zero, essentially by applying a stair case transformation like: > > You can do that by multiplying by 'k', subtracting 0.5*k and clamping > to [0,1[.
Actually, looking at the code, this is precisely what lp_build_brilinear_lod should be doing (albeit a bit more efficiently). It does not do a log2, as you implied earlier. log + brilinear is done by lp_build_brilinear_rho and not lp_build_brilinear_lod. Olivier, please look at the failure again, and confirm exactly what's the problem: does lp_build_brilinear_lod have a bug, does the assumption that clamping is not necessary not old, or is the piglit test too strict for bri-linear? > The question is whether you really want to do something > like that for explicit lod, where the user supposedly exactly knows > what he wants. "textureLod" is not used often at all[1], so one can > think that when it's used you'd better do it precisely. Maybe, but I'd rather not remove an optimization for the sake of a test. If it gets to that point, then I'd prefer make brilinear optional based on mipmaps being properly constructured mipfilters or not. Either way, I wanna fully understand what's going wrong before deciding. Jose _______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
